Vehicles may experience fluctuation in engine torque, manifested as a vehicle oscillation, and which may be referred to as surge. Surge may be caused by poor combustion stability due to a variety of engine operating conditions, including air-fuel ratio, burnt gas amount, fueling, and ignition timing. Poor combustion stability may be caused or aggravated by changes in environmental factors including ambient temperature, altitude, humidity, and others.
One example approach for addressing surge in a lean burn engine adjusts air-fuel ratio. For example, in U.S. Pat. No. 5,857,445, the engine control is switched from a lean combustion state to a stoichiometric combustion state in response to surge. In particular, changes in engine speed provide a surge index, which is then used to adjust the fuel injection amount, and thus the air-fuel ratio.
However, the inventors herein have recognized disadvantages with such an approach. For example, if combustion instability occurs due to reduced or excessive burnt gases in the engine cylinder, then adjusting air-fuel ratio may not fully reduce the surge, but rather reduce fuel economy.
In one approach, the above issues may be addressed by a method for operating an engine of a vehicle, the engine having a combustion chamber, comprising: controlling a stability of the vehicle in response to a vehicle acceleration, and selectively adjusting dilution in the combustion chamber of the engine to reduce surge in response to the vehicle acceleration.
In this way, it is possible to take advantage of the acceleration information for both stability control and surge control. Further, by appropriately adjusting dilution under appropriate surge conditions as indicated by the vehicle acceleration, surge may be addressed. In one specific example, dilution may be adjusted by adjusting intake and/or exhaust valve operation of engine cylinders. Additionally, or alternatively, dilution may be adjusted by adjusting an amount of exhaust gas recirculation and/or exhaust gas recirculation cooling.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.